The present invention relates to a projection pad using a liquid crystal panel in which a transmission-type liquid crystal panel is placed between a light source and a screen, and an image displayed on the surface of the liquid crystal panel is displayed on the screen.
Heretofore, various kinds of articles of this kind placed on an OHP (overhead projector) for projecting on a screen are commercially available. As the cooling mechanisms, a so-called Silocco blower of a cylindrical shape is used (for example, DATA DISPLAY DD-2000, manufactured by Eiki Kogyo), and two axial flow blowers (for example, SUPER VIEW PWS 5156A, Toshiba) were used to cool the inside of the projection pad by means of external air.
Further, for the control of the projection pad per se, i.e., control of input information instructing the operation of the projection pad such as luminance control, reverse display, etc.) there may be considered two ways, i.e., a remote controlling method and a method of providing switches, variable resistors, etc. for each control function.
However in the conventional cooling mechanism for the projection pad, if a Silocco blower is used, the size is relatively large (diameter is large and the length is long for the cylindrical shape), making it difficult to reduce the size and the thickness of the system. Further, when a plurality of axial blowers is used, the space requirements are large, which hinder reduction of the size.
Furthermore, for the control of the projection pad per se, if the remote controller sensor is mounted on a control circuit substrate, since the sensor is placed on the circuit substrate, reduction of size becomes difficult. Further, in the method of providing switches, variable resistors, etc. for each of the control functions in the projection pad, a large area is required for the lay out of parts such as switches or variable resistors and, in addition, such a arrangement increases the thickness and the controlling mechanisms have to be accessed in a state attached to an outer casing of the pad. Accordingly, the shape of the outer casing is complicated and high accuracy is necessary for the relationship between the outer casing and the control circuit, thereby hindering the reduction of the size and the thickness, as well as increasing labor for the assembling operation.
Further, in the apparatus of this kind, it is necessary to prevent the occurrence of radio wave interferences and countermeasures such as disposing electromagnetic shielding structures to the outer casing, etc. have been applied. Then, the shield plate hinders the reduction of the size and the thickness, as well as tends to worsen ventilation.